Image forming apparatus for simultaneous transfer and fixing of images

Abstract

An image forming apparatus such as a printer and a copying machine, employs a simultaneous transfer and fixing method to obtain a highly lustrous image of high image quality, free of uneven lusterand disordered pixels over the entire density area. Assuming the outside diameter of the convex side roll to be R (mm), the hardness of hardness test of durometer type A and the thickness of the surface layer of the concave side roll to be HR (degree) and dR (mm) respectively, the hardness of hardness test of durometer type A and the thickness of the surface layer of the toner image carrier in contact with the recording medium to be Hb (degree) and db (μm) respectively, and the nip width to be N (mm), the material and thickness of each surface layer for these two rolls and the intermediate transfer belt are selected so as to satisfy the following relationship: (Hb/HR)>0.8566 Ln{(N.sup.2 /R)·(db/dR)}-0.5077 where Ln<X> represents natural logarithm of X.

What is claimed is: 
     
       1. An image forming apparatus, comprising: an endless toner image carrier carrying a toner image;   a recording medium;   transfer fixing means for bringing said recording medium into contact with the toner image on said toner image carrier, heating said toner image, and transferring and fixing said toner image on said recording medium;   said toner image carrier having a surface layer on a side in contact with said recording medium;   said transfer fixing means having a first rotator which comes into contact with a back of said toner image carrier, and a second rotator for compressing said toner image carrier and said recording medium with said toner image interposed between said first rotator and said second rotator, said first rotator and said second rotator each having a heat-resisting layer on a respective surface; and   a hardness of at least one of the heat-resisting layers of said first rotator and said second rotator being equal to or lower than a hardness of the surface layer of said toner image carrier.   
     
     
       2. An image forming apparatus as defined in claim 1, wherein the surface layer of said toner image carrier is elastic. 
     
     
       3. An image forming apparatus as defined in claim 2, wherein the surface layer of said toner image carrier is composed of silicone copolymer. 
     
     
       4. An image forming apparatus as defined in claim 2, wherein the surface layer of said toner image carrier is composed of fluoro rubber. 
     
     
       5. An image forming apparatus as defined in claim 1, wherein the heat-resisting layer of at least one of said first rotator and said second rotator is elastic. 
     
     
       6. An image forming apparatus as defined in claim 5, wherein the heat-resisting layer of at least one of said first rotator and said second rotator that is elastic is composed of rubber elastic bodies. 
     
     
       7. An image forming apparatus, comprising: an endless toner image carrier which moves in a predetermined direction and carries a toner image;   a recording medium;   transfer fixing means for bringing said recording medium into contact with the toner image on said toner image carrier, heating said toner image, and transferring and fixing said toner image on said recording medium;   said toner image carrier having a surface layer on a side in contact with said recording medium,   said transfer fixing means having a first roll which comes into contact with a back of said toner image carrier, and a second roll for compressing said toner image carrier and said recording medium with said toner image interposed between said first roll and said second roll, said first roll and said second roll each having a heat-resisting layer on a surface respectively, and   a material and thickness of each heat-resisting layer of said first roll and said second roll and said surface layer of said toner image carrier satisfy the following relationship:   (Hb/HR)>0.8566Ln{(N.sup.2 /R)·(db/dR)}-0.5077     where Ln{X} represents the natural logarithm of X, assuming an outside diameter of a roll having a heat-resisting layer of the first roll and said second roll to be R (mm), a hardness determined by a durometer type A hardness test and a thickness of the heat-resisting layer of the other roll of said first and second rolls, which is different from the roll having said heat-resisting layer with higher hardness, to be HR (degree) and dR (mm) respectively, a hardness determined by the durometer type A hardness test and a thickness of the surface layer of said toner image carrier to be Hb (degree) and db (μm) respectively, and a nip width, equal to a length of said toner image carrier in the predetermined direction, of a nip portion which is formed when said first roll and said second roll are pressed against each other, to be N (mm).     
     
     
       8. An image forming apparatus as defined in claim 7, wherein the surface layer of said toner image carrier is elastic.   
     
     
       9. An image forming apparatus as defined in claim 8, wherein the surface layer of said toner image carrier is composed of silicone copolymer. 
     
     
       10. An image forming apparatus as defined in claim 8, wherein the surface layer of said toner image carrier is composed of fluoro rubber. 
     
     
       11. An image forming apparatus as defined in claim 7, wherein the heat-resisting layer of at least one of said first roll and said second roll is elastic. 
     
     
       12. An image forming apparatus as defined in claim 11, wherein the heat-resisting layer of said first roll and said second roll that is elastic is composed of rubber elastic bodies.